Method of preparing hypochlorites



Patented May 9, 1939 UNITED STATES PATENT OFFICE METHOD OF PREPARINGHYPOCHLORITES Irving E. Muskat, Akron, and George H. Cady, Wadsworth,Ohio, assignors to Pittsburgh Plate Glass Company, Allegheny County,Pa., a corporation of Pennsylvania No Drawing. Application April 14,1937, Serial No. 136,804

11 Claims.

that is, it contains one hypochlorite group and one chlorine atom permolecule; while true calcium hypochlorite is represented by the formulaOCl that is, it contains two 0C1 groups for each atom of calcium. Sincethis group constitutes the active radical of the compounds, true calciumhypochlorite has a much greater oxidizing value than bleaching powder.This oxidizing power is usually expressed in terms of active chlorinecontent; that is, twice the weight of the hypochlorite chlorine dividedby the weight of the sample. Multiplying this figure by gives the activechlorine percentage. True calcium hypochlorite has a theoretical activechlorine content of 99.2%, while the ordinary bleaching powder ofcommerce has an active chlorine content of approximately 35-38%. Thereis, therefore, a great advantage with the true hypochlorite with respectto its oxidizing strength, its purity, and shipping, storing andhandling costs as compared with bleaching powder. In addition, truecalcium hypochlorite is usually more stable. This advantage has spurredmany efiorts to prepare true calcium hypochlorite. Products containingfrom 65% to 72% active chlorine are now articles of commerce, but theyobviously fall short of being pure calcium hypochlorite with its activechlorine content of 99.2%.

In accordance with the present invention we have found that chlorinemonoxide at a temperature above about 25 C. preferably in the presenceof a gaseous diluent may be caused to react with calcium hydroxide toform a product containing a very high percentage of true calciumhypochlorite and, therefore, possessing a substantially higher activechlorine content and greater stability than any product now available onthe market. The treatment may be carried out with desirable resultsusing mixtures of chlorine and chlorine monoxide.

Theoretically, the reaction proceeds as follows:

Chlorine monoxide may conveniently be prepared by contacting chlorinegas with mercuric oxide or by contacting chlorine with soda ash orNaHCOa and in the presence of a small amount of moisture (e. g. lessthan 20% by weight). The reactions involved in the latter method may beexpressed by the equations:

In case sodium bicarbonate (NaHCOs) is employed, water is supplied bythe reaction.

The chlorine monoxide may be prepared in either liquid or gaseousmedium. If a liquid medium is employed it is liberated from the mediumfor subsequent transfer to a gas diluent by distillation. If it isprepared in a gaseous medium, the latter may act as the diluent duringthe subsequent reaction with lime. Convenient embodiments of thesemethods are disclosed in co-pending applications to George H. Cady,Serial No. 190,618, filed February 15, 1938, and to Irving E. Muskat andGeorge H. Cady, Serial Nos. 136,802 and 136,803 filed April 14, 1937.

Chlorine monoxide, produced in known manner, may be passed over oragitated with hydrated lime in powdered form. Preferably it is dilutedby at least an equal volume of inert materials such as air or nitrogen.Chlorine may also be present in the reaction mixture. This elementnormally reacts with hydrated lime to form bleaching powder or calciumchloride in admixture with calcium hypochlorite. However, when chlorinemonoxide is present, the bleaching powder or calcium chloride isconverted largely into calcium hypochlorite.

Small amounts of oxides of chlorine other than chlorine monoxide may bepresent in such small amounts as not to interfere in the reaction. Thetemperature may be maintained at any value above 25 C., but we prefer tokeep it between 30 and 50 C. However, higher temperatures up to C. orabove are contemplated. Alternatively the reaction may be carried outbelow 25 until the reaction has gone as far as it will at thattemperature, and then be completed at temperatures above C. This givesas good a product as that produced entirely at the higher temperatures.Proper control of the temperature is attained by any convenient means.

The hydrated lime used may be prepared in known manner by slakingcalcium oxide with water. The calcium oxide should preferably be activeand of good purity to insure a final product with a high percentage ofcalcium hypochlorite. Lime of commercial quality yields a good product.

It is obtained as a powder by slaking quicklime with water in an amountinsufficient to form a paste or slurry. Usually the amount of eitheruncombined calcium oxide or Water in the powder is not large, forexample, greater than about 20%. However, considerable variation issometimes permissible. Because of its small reactivity toward chlorinemonoxide, however, a large excess of calcium oxide is preferably to beavoided. On the other hand, the proportion of water may be large and thelime may be suspended in the form of a fluid slurry. When a solution orsuspension of calcium hypochlorite is prepared from milk of lime, it ispreferred that the amount of chlorine monoxide and chlorine should belimited to such an extent that the lime is not completely used up;otherwise, the calcium hypochlorite will decompose rapidly. If theproper precautions are taken it is possible to prepare solutions orsuspensions from which solid calcium hypochlorite may be separated byfiltration, evaporation, crystallization or by any suitable combinationof these operations.

Counter-current flow during contact of concentrated chlorine monoxidewith dry calcium hydrate is usually attended by excessive formation ofchlorate of lime and chlorine gas. However, when the chlorine monoxideis properly diluted with such gas as air this tendency is substantiallysuppressed, and counter-current flow is both permissible and desirable.

During the reaction, agitation alone, or accompanied by grinding inorder to expose fresh surfaces of the lime particles, is advantageous.Any convenient device, for example a ball or tube mill, is suitable forthe purpose.

The products manufactured by the above processes usually contain water,which should be removed in order that the stability of the calciumhypochlorite may be increased. Flash drying or vacuum drying may beresorted to. A substantially dry product is formed when the preparationof the calcium hypochlorite involves the use of chlorine monoxide, mixedwith inert gases, at temperatures in the neighborhood of 100 C. orhigher.

In the processes described in this application it is usually, though notalways, found that chlorine and, at times, chlorine monoxide remain inthe inert gas; consequently, it is desirable that the gas should becontinually recirculated, with suitable additions of chlorine monoxide,within the system in order that the loss of valuable materials may beminimized.

The following examples will serve to show the operation of our process:

1. A gas containing nine volumes of air to one volume of chlorinemonoxide was passed over substantially pure, active hydrated limemaintained at C. in a suitable agitator. After a slight excess ofchlorine monoxide had been passed over the lime, the product was driedand contained 82.5% active chlorine.

2. In another run the lime was held at 20 C. until some chlorinemonoxide began to pass over the lime without absorption. The.temperature was then raised to 40 and more chlorine monoxide added.After a small excess of chlorine monoxide had been used the productobtained, when dried, contained 85.6% available chlorine.

3. In a run under the same conditions except that a reaction temperatureof 10 C. instead of 40 C. was employed, and a large excess of chlorinemonoxide was passed, a product was obtained containing only 67.7% ofactive chlorine. This illustrates the eiiect of low temperatures in thereaction.

The reaction has been described with particularity in connection withthe preparation of calcium hypochlorite. However, the process may alsobe' employed in the preparation of hypochlorites of sodium, potassium,barium, strontium, etc. In such case the hydroxide of the desired metalis substituted for calcium hydroxide. Similarly, the process is notlimited to the treatment of hydroxides of these metals but may beapplied to the treatment of other reactive alkali and alkaline earthmetal compounds to produce the corresponding hypochlorites. For example,the chlorides of these metals such as calcium chloride or bleachingpowder may be treated with chlorine monoxide in accordance with ourinvention to produce stable compounds of high active chlorine content.

The embodiments of the invention herein described are to be consideredas exemplary. Numerous modifications may be made therein withoutdeparture from the spirit of the invention or the scope of the appendedclaims.

What we claim is:

1. A process of preparing calcium hypochlorite which comprisescontacting solid calcium hydroxide with chlorine monoxide in thepresence of an inert diluent gas and maintaining the temperature above25 C. during at least a portion of the process.

2. A process of preparing calcium hypochlorite which comprises admixingchlorine monoxide with air and then passing the mixture through dry limeat a temperature between 25 and 50 C.

3. A process of preparing calcium hypochlorite which comprises passing amixture of chlorine and chlorine monoxide and an inert gas through aslurry of lime.

a. A process of preparing calcium hypochlorite which comprisescontacting solid calcium hydroxide with chlorine monoxide at atemperature above 25 C.

5. A process of preparing the hypochlorite of a metal of the groupconsisting of the alkali and alkaline earth metals, comprisingcontacting a solid hydroxide of the metal with chlorine monoxide gas ata temperature above 25 C.

6. A process of preparing the hypochlorite of a metal of the groupconsisting of the alkali and alkaline earth metals which comprisescontacting a solid hydroxide of the metals with chlorine monox de gas inthe presence of a diluent gas at a temperature initially below 25 C. andthen when the reaction to form the hypochlorite slows up raising thetemperature above 25 and con tinuing the reaction.

7. A process of preparing the hypochlorite of a metal of the groupconsisting of the alkali and alkaline earth metals which comprisescontacting a solid hydroxide of the desired metal with chlorine monoxidegas at not substantially less than 100 C, in the presence of a gaseousdiluent whereby to produce essentially dry hypochlorite.

8. A process of preparing the hypochlorite of a metal of the groupconsisting of the alkali and alkaline earth metals comprising contactingthe hydroxide of the desired metal with chlorine monoxide containingsubstantial amounts of chlorine and. at a temperature aboveapproximately 25 C.

9. A process of preparing stable hypochlorites of the metals consistingof the group alkali and alkaline earth metals which comprises treating areactive hydroxide of said group with a mixture of chlorine and chlorinemonoxide.

10. A process of preparing stable calcium hypochlorite of high activechlorine content which comprises treating calcium hydroxide with amixture of chlorine and chlorine monoxide.

11. A process of preparing calcium hypochlorite which comprises treatinga solid lime containing moisture with chlorine monoxide at a temperatureabove 25 C.

IRVING E. MUSKAT. GEORGE H. CADY.

